This invention relates to electroforming mandrels. More particularly, this invention relates to a cylindrical electroforming mandrel having a removable thin wall sleeve fitted thereover which is especially useful for the electroforming of a nickel xerographic substrate.
In the usual practice of xerography, a latent electrostatic image of an object is formed on a recording medium or substrate called a xerographic plate. The xerographic plate may in turn comprise a thin layer of photoconductive insulating material, such as selenium, on a conductive metal backing such as brass or aluminum. The latent electrostatic image formed on the photoconductive material is developed into a power image which is subsequently transferred to a sheet of paper and affixed thereon to form a permanent print.
It has been previously proposed to utilize as the conductive metal backing portion of the xerographic plate, an endless flexible band, in which case the xerographic plate or substrate has been referred to as a xerographic belt. Examples of some typical xerographic machines and systems in which the latent electrostatic image is formed on a xerographic belt may be found in U.S. Pat. Nos. 3,045,644; 3,415,224 and 3,435,693.
Endless, flexible xerographic belts have been customarily made by joining or welding the ends of a thin strip of brass to produce an endless belt. The seam produced by joining or welding, however, has the disadvantage of reducing the overall strength and lifetime of the belt as well as requiring indexing of the printing cycle of the machine in which the endless belt is used. Indexing of the printing cycle is necessary to prevent the electrostatic image from being formed on that portion of the belt where the seam is located.
In U.S. patent application Ser. No. 250,894, Filed May 8, 1972, now U.S. Pat. No. 3,799,859, entitled "Electroforming Process" (D/3768) and Ser. No. 251,042, Filed May 8, 1972, now abandoned, entitled "Electroforming Apparatus" (D/3769), disclosure is made of an endless, seamless flexible belt suitable as a xerographic substrate. This endless seamless belt is made by an electroforming process which results in electrodeposition of a suitable metal such as nickel on the surficial portion of a cylindrically shaped mandrel. In the electroforming process disclosed in this application the mandrel is suspended in an electroplating solution and rotated therein, thus depositing a uniform thickness of metal on the surface of the mandrel. By expansion and contraction of the mandrel during alternate heating and cooling steps, the deposited nickel layer may be removed off the mandrel, since the mandrel employed has a different coefficient of expansion than the deposited nickel layer.
Hitherto, the mandrels used for this purpose have been fabricated by coating a cylindical aluminum forging first with various metallic electrodeposits for adhesion and then a top layer of chromium which is ground and polished to achieve the desired dimensions and surface finish. It has been found that this technique for making mandrels is slow and expensive and in so many cases the layer of top chromium is pitted thus making it unacceptable as a mandrel for production of a xerographic substrate. Also, it has been found that if the surface of the mandrel becomes damaged during subsequent use, all the coatings must be chemically removed and replaced with new coatings in order to provide a suitable surface for use in a high volume continuous electroforming operation. Thus, commercial usefulness of the electroforming process dictates that the most economical equipment be employed consistent with the desired quality in the final product, and to achieve this goal of economy it is necessary that the mandrel core member have the longest period of life in the process for which it was devised.
In view of the above consideration, it has been found that the objectives of economy, durability and quality could all be achieved by the use of a mandrel which comprises a hollow core member with a removable metal sleeve tightly fitted over the core member. Since the sleeve portion of the mandrel is the surface used for electrodeposition of the nickel belt in the event of damage to the surface, the sleeve may be conveniently replaced while retaining the core member. This allows more economical employment of the mandrel components while at the same time providing mandrel surficial and dimensional characteristics which are needed for electrodeposition of the nickel layer.
Therefore, in the development of a mandrel having a removable sleeve for electrodeposition of a nickel belt, it was unexpectedly found that all the desired objectives of commercial usefulness, reusability and high degree of functionality could be achieved by using a mandrel having not only a removable but a relatively thin wall metal sleeve, with the sleeve having a thickness of between about 10 and 60 mils. It is determined that a mandrel with such a removable sleeve not only still functioned perfectly in the process as would a mandrel without a removable sleeve but had the additional advantages of being more economical, and could be readily fabricated with a core member without any dimensional problems.
With regard to the dimensions of the mandrel, it should be pointed out that the dimensions and tolerances related thereto are directly related to quality of the belt electroformed thereon and its suitability as a xerographic substrate. For example, if a thicker metal sleeve were employed, it would be difficult to make a mandrel having the necessary cylindricity requirements and which is usable in the electroforming process because of difficulty in achieving conformance of the thicker sleeve to the dimensions of the core member. If however, a thin wall sleeve and particularly a sleeve within the recited thickness range is employed, it may be tightly fitted over the core member with no raised surface areas, to provide a surface which is nearly cylindrical as possible. The cylindricity of the mandrel not only controls the dimensions of the belt but in the event of an uncylindrical mandrel or one having non-uniform dimensions, the entire length of the belt becomes unusable in an imaging process because a resultant non-uniformity of the applied photoconductive material.
It is therefore an object of this invention to provide a new and improved mandrel structure which is of improved functionality insofar as the production of an endless, electroformed xerographic belt is concerned.
It is yet still another object of this invention to provide a cylindrical electroforming mandrel that is relatively easy and expensive to make and can be repaired easily if damaged.